Ever stricter legal specifications in respect of permissible pollutant emissions of motor vehicles, in which internal combustion engines are arranged, render it necessary to keep the pollutant emissions as low as possible during operation of the internal combustion engine. This can take place on the one hand by the pollutant emissions, which are produced during the combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine, being reduced.
On the other hand, exhaust gas after-treatment systems are used in internal combustion engines, which convert the pollutant emissions produced during the combustion process of the air/fuel mixture in the respective cylinders, into harmless substances.
To this end, exhaust gas catalytic converters are used, which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances.
Both the targeted influence of the generation of the pollutant emissions during the combustion and also the conversion of the pollutant components with a high degree of efficiency by means of the exhaust gas catalytic converter require a very precisely adjusted air/fuel ratio in the respective cylinder. The technical book “Handbuch Verbrennungsmotoren” [Combustion engine manual], publisher Richard van Basshuysen, Fred Schäfer, 2nd edition, Vieweg and Sohn Verlagsgesellschaft mbH, June 2002, pages 559 to 561, discloses a linear lambda controller with a lambda probe, which is arranged upstream of an exhaust gas catalytic converter, and a binary lambda probe, which is arranged downstream of the exhaust gas catalytic converter. A lambda set value is filtered by means of a filter, which takes the gas travel times and the sensor behavior into account. The thus filtered lambda set value is the regulating variable of a PII2D-lambda regulator, the control variable of which is an injection quantity correction. The signal of the linear lambda probe is converted into a detected lambda value by way of a stored characteristic curve. This characteristic curve is subjected to a correction by means of a trim regulator. The trim controller assigned to the trim regulator is embodied as a PI controller, which uses the after-cat probe exposed to less cross sensitivities, which is preferably assigned by a binary bistable sensor arranged downstream of the exhaust gas catalytic converter.
The trim regulator is used to monitor the catalytic conversion and fine tuning of the mixture.